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Auto Repair Questions - What's Your Problem?

Your idea of putting a TPI on a 283 is something we kicked around at a Car Craft bench racing session a while ago. The concept was to build a small-displacement small-block with a TPI manifold to pump up the torque for a daily driver engine controlled by a budget aftermarket EFI unit like the MegaSquirt or the private label version called the eMS-pro from Spectre Performance. The EFI would maintain the air-fuel ratio at 14.7:1 running down the road to get good gas mileage. Vortec iron cylinder heads would be a great choice, but the cost would go up because you'd need a Scoggin-Dickey Vortec TPI manifold (PN 12498060, $399.95 at Other alternatives for heads had to be those with 64cc chambers to keep the compression up. The least expensive new iron heads would probably be the World Products S/R Torquer iron heads with 2.02/1.60-inch valves (PN 042660-1, $799.98/pair, Last month we tested a pair of the new Patriot Freedom Series 64cc aluminum heads that sell complete for $795 a pair from Patriot (, so you might want to check that test as well. We compared them to a set of Vortec iron heads as the baseline and they came in just shy of the Vortec heads in terms of overall power; nevertheless they are decent aluminum heads for under $800 that would accept a TPI manifold.

One problem is that even with a 64cc chamber, 4.00-inch bore, 3.00-inch stroke, 0.040-inch head composition gasket, and 0.005-inch piston deck height, this will only generate 8.79:1 compression. This assumes boring the little 283 out with a 0.125-inch to a 302ci engine. Most 283- blocks will handle this additional 0.125-inch bore increase and still have decent wall thickness. To make more compression, you would have to go to a slightly domed piston.

For a cam, we'd go with a short-duration hydraulic flat tappet cam of around 210 degrees at 0.050-inch tappet lift again to make good cylinder pressure at lower engine speeds, where the engine could make some decent torque. Along with the TPI intake, this would be a great combination for torque and fuel mileage. It's an interesting idea for someone looking for a mileage-oriented small-block that would look cool and knock down 25-plus miles per gallon.

New Rat On The Block
Trevor Knill, via Car Craft e-mail: I have an 8.1L big-block out of an '04 Chevy HD truck. I would like to know if anyone makes an intake manifold for this engine. I would like to run a carburetor on it. I have noticed there is a block-off plate under the intake where the distributor would go, covering the distributor gear. I assume I can run a regular distributor in this motor. Any info would be greatly appreciated.

Jeff Smith: There's good news and bad news here, Trevor. The good news is that this 8.1L (496ci) Rat motor is going to become more and more prevalent in the junkyards as the years slip by because this is the new, GM large-displacement big-block. But for right now, that's about as far as the good news goes. We started digging into this engine and only found one shop that specializes in building these engines, a company called Raylar out of San Diego. We spoke with Raylar owner Ray Brogey, and he filled us in on the engine's details. The motor is based on the old Mark IV bore centers, and the bellhousing pattern is still the same, so you could bolt this big-block into a Chevelle or Nova. We hesitate to call it a Rat, but it still could be considered a part of the rodent family. The bad news is that the cylinder heads use an increased 18-bolt pattern that is different from the original MK IV, so the heads won't interchange, and beyond that, the intake manifold is also different because the intake port arrangement is symmetrical, like the Gen III/LS1 engines. No one makes a carbureted intake manifold for this engine, although Raylar does make a high-performance electronic fuel injection manifold for its marine applications.

The stock 8.1 employs a cast crank, forged 6.693-inch rods, and cast pistons with a 4.25-inch bore and a 4.37-inch stroke. Compression is 9.1:1 with an iron block and heads. The fuel-injection system is sequential, but Brogey says it's designed to make torque, and the heads are pretty tame right down to the net lash system. The motor comes with a hydraulic roller cam, but it also is different from the old Rat motor stuff since the firing order has been changed to the Gen III firing order (1-8-7-2-6-5-4-3). According to Brogey, if you want to start tuning on these engines, all the EFI and spark table information is set up just like the Gen III engines.

Raylar specializes in marine applications and sells several normally aspirated power packages that are designed to be incredibly durable and would be virtually indestructible on the street. Raylar also offers the only forged steel 4.50-inch (510ci) stroker crank for this engine along with Mahle forged pistons. Flow numbers on the Raylar aluminum head measure up to 370 cfm at 0.500-inch lift. Raylar engine packages can make 500-600 hp and upwards of 700 lb-ft of torque. Remember, these engines are designed to make power at around 5,000 rpm because they have to be able to run reliably at WOT all day long.

While all these parts are cool, because of the limited demand they will cost more than comparable Rat motor parts. As for a carbureted intake manifold, Brogey says your only real alternative is a custom aluminum sheetmetal manifold. They aren't cheap and are frankly a bit of overkill considering that the 8.1L cylinder heads are nothing special. Stock valve sizes for the 8.1L heads are 2.19/1.72. Our suggestion would be to sell this motor to somebody who could put it to good use as a replacement engine for his truck, and go out and buy a real Rat motor. In the long run, you'll make more power for a lot less money.

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Holley Performance Products
1801 Russellville Rd.
Bowling Green, KY 42101
KY  42101
Spectre Industries
Mr. Gasket (ACCEL)
10601 Memphis Ave. #12
OH  44144
Moroso Performance Products
San Diego
Scoggin-Dickey Parts Center
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